An internal combustion engine misfire occurs when an air/fuel mixture is improperly consumed in an engine cylinder. Misfire conditions can affect engine stability and emissions. Misfires must be diagnosed so that treatment procedures may be applied to minimize any resulting effect on stability or emissions. Misdiagnosis of misfire conditions results in unnecessary repair costs and in unnecessary inconvenience to the engine operator.
Several misfire diagnostics have been proposed. Typically, such proposals attempt to identify engine speed variation patterns characteristic of engine misfire conditions. Such characteristic misfire patterns can be difficult to identify at certain engine operating levels such that the diagnostic may be disabled at such operating levels or may be prone to misdiagnosis at such operating levels.
It would therefore be desirable to reliably diagnose engine cylinder misfire conditions at all engine operating levels.